The US military, under the direction of President Joe Biden, conducted airstrikes on Sunday against what it said were "facilities used by Iran-backed militia groups" near the border between Iraq and Syria.
Pentagon Press Secretary John Kirby said the militias were using the facilities to launch unmanned aerial vehicle attacks against US troops in Iraq.
Kirby said the US military targeted three operational and weapons storage facilities - two in Syria and one in Iraq.
He described the airstrikes as "defensive," saying they were launched in response to an "ongoing series of attacks by Iran-backed groups targeting US interests in Iraq."
"The United States took necessary, appropriate, and deliberate action designed to limit the risk of escalation - but also to send a clear and unambiguous deterrent message," Kirby said.